Precision inertial navigation systems typically require concentric sets of ball bearing supported gimbals which allow instruments to freely rotate in flight maneuvers and allow them to be manipulated for calibration. The embodiments of the previously referenced '184 Application, which is herein incorporated by reference, eliminate the need for gimbals and ball bearings by supporting the inertial sensor assembly with a spherically shaped gas bearing. The gas bearing allows rotation of the inertial sensor assembly in all axes with no wear due to contact between rotating surfaces. During the flight of a craft, the angular position of the inertial sensor assembly (sometimes also referred to as the attitude, or roll, pitch and yaw of the inertial sensor assembly) relative to the frame of the craft must be monitored at all times. However, because physical contact with the freely rotating, gas bearing supported, inertial sensor assembly is undesirable, the need arises to sense the position of the inertial sensor assembly without physical contact between the sensor and the assembly.
A typical globe of the Earth is one example of a three dimensional object that allows a user to readily identify coordinates on its surface by marking a visual coordinate system on its surface. The surface of a globe is first marked by a series of evenly space meridian lines running from the north pole to the south pole. These meridian lines establish the longitude coordinate of a point of interest. The surface of the globe is also marked by a series of parallel circles running east and west along the surface of the globe. Parallel lines establish the latitude coordinate of a point of interest. To identify the coordinates of any point on the globe, a user need only observe numerical markings printed on the two closest marked longitude and latitude lines and interpolate the coordinates of their point in interest. While a marking system with printed numerals allows a person to accurately identify the coordinates for any place on a globe, it is not optimized for real time dynamic control systems such as an inertial navigation system.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the specification, there is a need in the art for a contact free means to determine the angular position of a spherical object.